As a developer, my most important tools are a pen and a notebook

It's not romanticism and it's very important for me too. I spend a lot of my time drawing out what I'm trying to do before I actually try to do it. I tend to work on greenfield embedded projects though for context. Coding and debugging is hard to get good at and are obviously important, but you still need to figure what to actually build and those tools won't get you there. For me, I use a pen and paper to actually figure out what I need to do.

I had to work on a coding project with a serious geometric problem in the core, and no amount of thinking over code itself could help, whereas on paper, I could find the solution easily. And implementing it in code didn't progress, until I wrote down all the formulae, in sequence, on paper too.

As I like to say, I do most of my programming before I touch a keyboard.

The single most powerful thing I do is ask questions and write down the answers. When I want to understand a system this is the fundamental step that cannot be skipped. How crucial it is that I understand the system will tell me how formal I need to be in my thinking. If it's a basic web application or a report I need to generate it's a simple, informal note. If we're talking about a critical system that's distributed and requires high-availability with hard limits on processing time and the consequence of getting things wrong is that businesses and people lose money/property? Then I'll bust out the mathematics and model things formally.

I've experimented as well with writing code on paper first. This doesn't work so well with procedural languages without some form of shorthand/formalism. It works much better with statically-typed functional programming languages. When using such languages I mostly need to reason about the types: the implementation is a matter of filling in the holes which can be done when I'm at the keyboard. The more I learn to "think in types," the better this works but I'm not super great at it yet.

Notebooks are where it all begins.

I also use notebooks to journal my work. I use the bullet journal system to keep track of my work. Keeping it on paper forces me to sit in front of it and physically remind myself of my tasks. It helps me stay focused on the day to day activities and not lose track of my longer-term goals. After using one long enough this way it becomes a chronicle of my work. Handy for performance review season. A great deal of programming work comes out of these journals.

Some folks prefer digital tools and that's fine and dandy. I'm just old school and prefer physicality. Paper and pen work on the level my brain works on and gives me a break from screen, keyboard, and constant stream of notifications. Room and freedom to think without interruptions is important and useful.

This is one of the reasons that I actually take notes in three different media: paper notebooks, an old-school digital voice recorder, and in text files. Different media have different advantages and disadvantages and represent different ideas for more readily.

I have used the voice recorder less over the years but I find it optimal when time is limited and I have to move onto something else. Part of using a voice recorder as a medium is listening closely afterwards and writing down what I said in a different manner (either in a more permanent paper notebook or digitally in a text file). And yes, each iteration transforms the idea at least somewhat. It gives you the chance to see the idea in a different way.